1. Field of the Invention
The present invention relates to means for and methods of detecting leaks in tanks for storing gasoline, oil and the like.
2. Description of the Prior Art
Leakage of a small amount of liquid from underground liquid storage reservoir such as used to store gasoline in typical petroleum service stations and the like is difficult to efficiently determine. However, the National Fire Protection Association considers any such leakage of over 1.2 gallons per day to be intolerable. Heretofore, a number of procedures and devices have been used to detect leaks in liquid storage reservoirs. Among these prior procedures and devices are those that measure product temperature changes during test periods so that expansion or contraction of the liquid might be taken into consideration and related to changes in liquid volume and/or level in determining whether or not a reservoir is leaking. White, U.S. Pat. No. 3,580,055 discloses the use of a single electronic temperature responsive sensing device (thermistor) in an electrical and/or electronic circuit and requires a fluid circulating system which continuously circulates fluid from the tank and back to equalize the temperature of the fluid in the tank and permit compensation for temperature variations in the system.
The present invention is an improvement of the inventor's prior leak detecting system for which U.S. Pat. No. 4,186,591 issued. The system taught by U.S. Pat. No. 4,186,591 includes means for measuring any change in the level of liquid in a liquid storage reservoir over a certain period of time and means for measuring any change in the temperature of the liquid in the reservoir over the same period of time. The temperature sensing means described in U.S. Pat. No. 4,186,591 includes a single thermistor element (it was pointed out in U.S. Pat. No. 4,186,591 that a plurality of thermistor elements could be used), a source of electrical power and means for measuring the amount of electrical power passing through the thermistor element.